1. Technical Field
The present invention relates to an ink composition, a recording method using the same, and a recorded matter thereby. Further specifically, the invention relates to an ink composition excellent in viscosity-temperature characteristics of ink, cockling and curling characteristics, and fixation properties, and relates to an ink jet recording method and a recorded matter.
2. Related Art
An ink jet recording system is a recording method for conducting printing by letting ink droplets fly from an ink jet head and attach them to a recording medium such as paper. Because of recent innovative progress in ink jet recording technology, the ink jet recording method has been also used in the field of highly fine image recording (printing), which was ever achieved only by photograph or offset printing.
The ink used in such an ink jet recording method is required to have adequate physical characteristic values to be discharged from an ink jet head and controlled as fine ink droplets. In particular, it is preferred to have a lower viscosity compared to that of a common printing ink composition. As one method therefor, ink containing a high amount of water (aqueous ink) is widely used.
Paper exclusively used for ink jet printing has an ink-absorbing layer for absorbing ink and thereby has a problem of high cost. Plain paper such as copy paper does not have the ink-absorbing layer and therefore is inexpensive, but has problems relating to penetration of ink such as strike-through (a phenomenon that printed ink passes through a recording medium and the image appears on the reverse face) and bleeding and also problems of curling of plain paper after printing an image and unevenness (cockling) of a printed area.
Against the above-mentioned problems, a recording method by measuring wetting time to a recording medium and absorption coefficient by a Bristow method and using ink of which penetration properties are improved is proposed (for example, refer to JP-A-10-316915). However, in this method, since the colorant in the ink also penetrates into plain paper together with the ink, the method has problems that the printing quality is insufficient and that strike-through is significant. In particular, the method is unsuitable for both-side printing.
Furthermore, methods for improving the curling and the cockling of paper are proposed, for example, an ink jet ink containing a specific amide compound, pyridine derivative, imidazoline compound, or urea compound as a curling-preventing agent (for example, JP-A-9-176538) or an ink jet recording method for optimizing curling balance by providing a solution containing water to the reverse face side of an image-printing face (for example, JP-A-10-272828). However, known curling-preventing agents cannot prevent cockling and are also insufficient in curling preventing effect. In addition, the method providing a solution containing water to the reverse face has problems that a large printing apparatus is necessary and also that cockling becomes serious.
Furthermore, instead of the aqueous ink, non-aqueous ink has been also investigated. The non-aqueous ink has advantages that curling and cockling tend to not occur even in printing on plain paper, compared to aqueous ink. In such non-aqueous ink, since the ink containing a volatile solvent has an environmental problem, recently, it has been tried to use a solvent derived from vegetable oil that is low in environmental load (for example, JP-A-2005-132907). However, since such oil-based ink has high penetration properties to plain paper, the oil-based ink has problems that the printing quality is insufficient and that strike-through is significant. In particular, the ink is unsuitable for both-side printing.
Against these problems, an ink containing a low amount of water has been proposed. By reducing the content of water in the ink, the content of other components contained in the ink is increased. Depending on the components contained in the ink, the ink has a problem that the viscosity of the ink at low temperature (for example, at 10° C.) tends to increase, and conversely, the viscosity at high temperature (for example, 40° C.) tends to decrease.
If the viscosity is largely increased or decreased with temperature, the voltage signal applied to an ink jet head becomes too high, or treatment becomes complicated.